The present invention relates to an arrangement for discharging liquid medium under a high pressure from a feed pipe having a tubular end portion.
It is known in the prior art to use such an arrangement for extraction of minerals such as rock, coal, etc. The arrangement may be used alone for this purpose of in combination with a mechanical cutting tool such as a chisel.
One of the specific features of such an arrangement resides in supplying liquid medium (e.g. water) under an extremely high pressure, i.e., up to many thousand bars, through a jet. Thus, should the arrangement be located adjacent to the surface to be cut the high pressure water jet becomes extremely efficient for mining purposes. It is known to use a jet made of sapphire or diamond in form of a plate disc with a very small throughgoing hole. The outlet hole is advantageously smaller than 1 mm in cross-section, and preferably between 0.2 and 0.8 mm. The jet is mounted in a jet holder which in its turn is fixed in a jet support which has an inner recess so shaped as to increase the pressure of the liquid medium considerably even before the same enters the jet. In this case the jet tends to additionally and utmostly increase the speed (i.e., pressure) of the turbulent stream of the liquid medium. Thus, if the liquid medium pressure is 3000 bar and the cross-sectional dimension of the jet outlet is 0.3 mm the speed of the liquid medium exiting the arrangement is above 700 m/sec and the liquid medium discharge (i.e., water consumption) increases up to 3.2 l/min. It is also possible to increase these numbers even further if the liquid medium pressure is correspondingly increased and the cross-sectional dimension of the jet outlet is decreased to 0.2 mm. The kinetic energy of the exiting high pressure water jet is so great that with its help and depending upon the actual rock resistance (i.e., density) the rock surface tends to crack and form splits or breaks with a depth up to 30 mm.
The purpose of the arrangement is to cut with a high-pressure waterjet concentric annular splits in the rock surface of a drift (i.e., a driving gallery). The rock medium located between the splits is withdrawn by a rock drill (e.g., annular drill, mortising drill, etc.). Thus, when the arrangement for discharging the liquid medium under a high pressure is combined with a mechanically operated cutting tool the extraction is considerably facilitated; therefore the extraction productivity may be correspondingly increased. In order to obtain the best possible extraction results the liquid medium jet has to be located immediately adjacent to the mechanically operated cutting tool and as close to the surface to be cut as possible. Due to such arrangement of the high-pressure water jet it becomes possible to utilize so-called hydraulic "wedge effect", so that the high pressure water enters small fissures and cracks which are developed on the surface to be cut by the cutting tool simultaneously with advancing of the tool into these fissures and cracks. In other words the high pressure water jet considerably facilitates the advancement of the cutting tool into the surface to be cut.
Since the best possible effect of the high pressure water jet is achieved when the latter is located immediately adjacent to the surface to be cut (that is at the surface which is cut by the chisel during its working strokes), it is desirable to locate the high pressure water jet in front of the cutting tool (i.e., chisel) and before the surface to be cut or, depending upon the desirable eventual result, directly on the chisel with the jet directed forward towards the surface to be cut.
It has been recognized, however, that due to extremely high pressure of the liquid medium it is quite difficult to manufacture the jet with sufficiently small cross-sectional dimensions so as to be able to install the jet on corresponding grooves provided immediately on the face edge of the chisel or on the chisel itself in order to facilitate and increase the extraction productivity.
It is known in the prior art to provide a jet with a connecting coupling for detachably connecting the jet to a feed pipe. The jet projects outwardly beyond the feed pipe. The feed pipe itself due to the high pressure of the liquid medium has to have relatively thick wall. If it is desired to maintain the outlet hole of the jet, for example, 0.3 mm then the cross-sectional dimension of the feed pipe with the connecting coupling (i.e., for connecting the jet to the feed pipe) constitutes about 0.3 mm. Obviously, it is quite difficult to locate the jet having the overall cross-sectional dimension of 30 mm immediately adjacent to the surface to be cut, as is required in order to obtain the best extraction results. It is almost impossible to install such a jet arrangement on the recess provided on the chisel. Therefore, it is impossible to supply pressure water jet directly into the fissures and cracks in the surface to thereby advantageously utilize the above mentioned hydraulic "wedge effect".
However, if the high-pressure water jet is not located immediately to the surface to be cut, then its efficiency in facilitating the extraction process is considerably limited.